Deep Heat Mining Basel
Deep Heat Mining Basel , also known as the Deep Heat Mining project , was a joint project by Geopower Basel AG and Geothermal Explorers Ltd. for the generation of electricity and heat from geothermal energy (geothermal energy) by means of deep drilling in the Basel area . The Basel facility is a pilot project as part of the Swiss Deep Heat Mining Project . The project was definitely discontinued in 2010.
The planned system should work on the principle of a flow heater . A pump first presses water to create a system of fissures in the earth's crust ( hot dry rock process or hot fractured rock process ). Cold water is pumped into the cavities obtained, the water heats up and is pumped back to the surface.
This process was to be used commercially for the first time in Basel. The water heats up to 200 degrees Celsius and is then pumped back to the surface of the earth. A heat exchanger extracts the energy for the production of electricity with turbines in a closed system , the remaining heat is dissipated as district heating. Investments of around 80 million Swiss francs were budgeted for the construction of the plant. In addition to Geopower Basel AG, the cantons of Basel-Stadt and Basel-Landschaft and various energy service providers were involved in the construction.
The location was chosen because of the special tectonic location. Basel lies at the southeast end of the Upper Rhine Rift . This was created at a point where around 40 million years ago southern Germany rose to form a large vault and the earth's crust was stretched. This activity subsided around 10 million years ago and led to a wide rift and a subsidence of several thousand meters between the Vosges and the Black Forest . The strain caused a natural circulation of hot pore water in the rock. For example, rock can be found at a depth of five kilometers that, at 200 degrees Celsius, is suitable for heat recovery.
The suitability of the Basel region for this project, as Energie Zukunft Schweiz claimed on its website in 2007, was confirmed in 2001 by exploratory boreholes to a depth of 2700 meters.
In 2005 the first test drilling took place at Zoll Otterbach with a depth of 2700 meters. This hole formed the basis for a feasibility study on which the project was based. The project envisaged that three test drillings with a depth of between 2,700 and 5,000 meters in the Kleinhüningen and St. Johann area would be carried out over a period of three years . The aim was to prove that the rock can actually be fissured with the help of injected water. The associated power plant should be built by 2009.
Induced earthquake ( induced seismicity )
In December 2006, a test borehole to a depth of 5000 m was carried out in Kleinhüningen. After that, water was pumped into the rock to fracture the rock and increase its permeability. It was expected that small earthquakes, so-called microquakes, would occur. However, these earthquakes should only be able to be recorded by highly sensitive measuring devices and at the same time provide information about the success of the project.
When water was injected in December 2006, there were not only the expected smaller earthquakes, but also stronger, noticeable earthquakes up to a magnitude of 3.5 (local Richter magnitude ). An earthquake with a magnitude of 3.4 occurred on the evening of December 8, 2006 . Smaller vibrations were already noticeable during the day. As a result, there were numerous smaller earthquakes with a magnitude of 0.5 to 1 and another earthquake with a magnitude of 3.1 on January 6, 2007, although the water pressure in the borehole was reduced immediately after the first severe tremor. The seismic tremors had not subsided by February 2007. On January 6, January 16 and February 2, further earthquakes with magnitudes over 3 occurred, and on March 20 one with a magnitude of 2.9.
There was no major damage, but the population was unsettled. Geopower Basel AG had the derrick dismantled after the event and stopped the project for the time being. The Basel authorities re-examined the project and a discussion about its continuation developed. Geothermal experts said in the newspaper Die Welt that these artificially triggered earthquakes could reduce the risk of a new Basel earthquake . According to the Swiss Seismological Service , however, this effect is negligible.
The public prosecutor's office in Basel raised against the managing director of Geothermal Explorers Ltd. Accusation. The court later acquitted the geologist.
It was decided to discontinue the project because, according to an existing risk analysis, further severe earthquakes and damage of around CHF 40 million would have been expected during the plant construction alone. In addition, damage of around six million Swiss francs per year can be expected during operation.
Due to an increase in micro-earthquakes, the borehole in Kleinhüningen has been briefly opened weekly since July 2017 to relieve pressure. In the autumn the pressure was completely relieved; the borehole is now left open to prevent it from rising again.
- The deep heat mining project in Basel. Information from the Swiss Seismological Service about the project
- Homepage of Geopower Basel AG (not updated since 2007)
- Geothermal Switzerland
- Documents on the canton's geothermal project
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- Deep Heat Mining and Seismology. The deep heat mining project in Basel, Swiss Seismological Service (SED)
- Technical and geological background. The deep heat mining project in Basel, Swiss Seismological Service (SED)
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